Robert_Charlton - 10:23 pm on Sep 4, 2010 (gmt 0)
PS to the above, to expand and clarify an important point about which there's a lot of misconception....
Keyword domain names that are 301 redirected have no SEO benefit in and of themselves. What may be beneficial is keyword anchor text in links currently existing on the web that point to those domains.
To get those links, you generally need either to have had relevant content online under those domains... or you need to be in control of the links. Google doesn't like your promoting a lot of domains and then removing and redirecting them, and Google can spot this on a link map.
If you were in control of the links in the first place, there's no point going through the charade of putting up a domain that had keywords in it and then taking it down. You're much better off just building relevant content on your main domain and getting links with relevant keywords to that content.